Wonders of Regeneration

(I originally wrote this May 01, 2007):

Several months ago (before I fully appreciated this species’ uncanny ability to master aquarium dividers), I discovered one of my largest Macrobrachium carcinus in the process of consuming a conspecific. Within the space of what was probably just a few minutes, the victim had lost all of its pereiopods, an antennal spine, much of its rostrum, and the forward fringe of its cephalothorax.

Hoping for the best, I immediately isolated it in a 10-gallon tank. Even in its grublike state, the shrimp was able to flutter clumsily forward; thankfully, neither gill tissue nor eyes had been scathed. Though the pearly gray of its wounds acquired black edges of necrotic tissue, the recovering patient remained as voracious as ever, first clutching food placed directly beneath its mandibles and later scooting about with its pleopods to secure sinking pellets.

Within three weeks, limb buds made their appearance. Shortly afterward, the shrimp underwent its first regenerative molt.

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I recall hearing about a New Zealand researcher who removed all of the the legs from a spider, then kept the animal on some moist cotton wool and fed it with a dropper until it moulted. The spider was able to regrow all its legs.

genghisprawn, was the attack shortly after a molt of the victim? How long takes the hardening of the new exoskeleton of M.carcinus in this size? Have you seen the consumption of the old skeleton?
And last but not least (to Christopher): Who removed the brain of the New Zealand researcher?
Thanks a lot in advance
Cheers, Robert

I can’t remember whether this was the case in this particular instance, but most of the cannibalism I’ve witnessed in captive Macrobrachium does indeed shortly follow molting of the victim.

The old exoskeleton is readily consumed — by a congener in the same tank if not by the original owner — but the terminal segments of the chelipeds (especially the hooked tips) are often left untouched or only gradually consumed. Although these parts would seem to be richly calcified, their structural reinforcement might just be too formidable.

Macrobrachium can move about with jackknifing flexes of the abdomen almost immediately after molting, and basic use of the limbs is regained within minutes. Small juveniles, at least initially, may prefer to hover or swim about using the pleopods (swimmerettes) instead of the walking legs, particularly if hungry neighbors are up and about. The exoskeleton is usually consumed within a matter of hours if the prawn is kept by itself, but, if secretive post-molt behavior is any indication, full hardening takes longer.

Thanks a lot for the informations. This species is known for beeing aggressive, as far as i know big males defending their territory. How is the density of specimens in your aquarium? How is the consistence of the fresh shed exoskeleton, can you easily break the connection between abdomen and carapax? I am searching for the right tagging method for M.carcinus
(micro-wire tags are to expensive)
Thanks in advance,
regards, Robert

Are you doing field work with M. carcinus? I would be interested to hear more.

The highest density at which I’ve kept M. carcinus is three young specimens in a partitioned US 55 gallon tank (210 liters: 120 x 32 x 53 cm). However, since the aquarium dividers didn’t reach all the way to the top, the prawns crawled out of the water to enter their neighbors’ compartments. After incidents like the one described in this post, I gave each prawn its own enclosure.

Unless one has very large tanks with lots of cover (PVC tubes or rocks and leaf litter), I think separate housing is the safest arrangement. Adult males often tolerate the presence of females; perhaps they also have some way of reducing aggression when low rainfall concentrates them in isolated pools.

The fresh exuvium is somewhat pliable and rubbery to the touch. Out of air, it quickly becomes brittle; if exposed to decomposition underwater, it acquires a jelly-like consistency within a few weeks.

After molting, the cephalothorax and the abdomen are still sufficiently connected for one to be able to take them out of the water in a single piece, but careless handling can separate them.